A fuel cell is an electrochemical conversion device that produces electricity from a fuel and oxidant that react in the presence of an electrolyte. A single fuel cell may include a membrane electrode assembly and two flow field plates. Single cells may be combined into a fuel cell stack to produce the desired level of electrical power. A fuel cell may include two electrodes, an anode and cathode, separated by a polymer membrane electrolyte. Each of the electrodes may be coated on one side with a thin platinum catalyst layer. The electrodes, catalyst and membrane together form the membrane electrode assembly.
Gases, e.g., hydrogen and air, may be supplied to the electrodes on either side of the membrane through channels formed in the flow field plates. Hydrogen flows through the channels to the anode where the platinum catalyst promotes its separation into protons and electrons. On the opposite side of the membrane, air flows through the channels to the cathode where oxygen in the air reacts with the hydrogen protons which pass through the membrane. The hydrogen dissociates into free electrons and protons (positive hydrogen ions) in the presence of the platinum catalyst at the anode. The free electrons are conducted in the form of usable electric current through an external circuit. The protons migrate through the membrane electrolyte to the cathode. At the cathode, oxygen from the air, electrons from the external circuit and protons combine to form water and heat.